Hematocrit is the concentration of red blood cells (RBC) in blood. The measurement of hematocrit values is of great importance in the assessment of the condition of a patient. The established method of measuring hematocrit is by drawing blood from the subject (patient). Various methods to optically measure hematocrit by optical or ultrasonic means have been attempted, e.g., during a dialysis treatment of a patient. In these situations, not only the level of hematocrit is of high importance but also the relative variation of this parameter. In order to provide an optimized but still safe dialysis treatment the change of the hematocrit or relative blood volume has to be monitored during the treatment. The attempts to monitor this have so far not resulted in any product that can measure the hematocrit without a special cuvette integrated in the transport tubing. The methods used so far have therefore increased the cost of every dialysis treatments since the transport tubing must be equipped with this single-use cuvette. The invention presented here does not require any special cuvette, instead it provides the possibility to measure the hematocrit, or monitor the change of relative blood volume directly on any standard dialysis transport tubing on the market without increasing the cost of each treatment.
1. Technical Field
The invention relates to measuring various blood constituents with optical means. Blood is irradiated with—preferably—near infrared or infrared light. Light scattering and attenuation of the light is measured and novel compensations for optical variations in the receptacle walls, flow etc. is used to calculate blood constituents such as hematocrit. The invention makes it possible to add the feature of hematocrit measurement without major alterations into any dialysis system. The addition of this feature makes blood volume measurements at hand.
2. Prior Art
Hematocrit has been measured with various methods since the beginnings of medical diagnosis. Continuous measurement is particularly useful during dialysis treatment. During the process of dialysis, liquids are extracted from the blood stream. As a result, hematocrit increases during the process. For the assurance of good quality in the dialysis treatment, the hematocrit value should be monitored, as this provides the care provider with essential information regarding the rate of extraction of fluids from the patient's bloodstream.
Various techniques have been presented in the field of optical measurements of hematocrit in blood. Several make use of the scattering effect RBC has on light passing trough blood in a vessel, cuvette or the like. Oppenheimer presents in U.S. Pat. No. 5,601,080 a method to measure the degree of scatter to derive blood constituents.
Other patents are U.S. Pat. No. 4,745,279 to Karkar, describing scattering effect of blood in a cuvette. U.S. Pat. No. 6,493,567 to Krivitski et al. describes a measuring instrument using one light emitting diode and one sensor. U.S. Pat. No. 6,064,474 to Wylie et al is another description of a hematocrit measuring method using the scattering effect RBC has on light. However the known methods and devices do not provide a satisfactory precision.